Shortstopping vinyl chloride polymerizations with nitriles



Patented Nov. 4, 1952 UNITED PATENT OFF-ICE Daily, New York-,'. Y.,

Jersey a corporation cf New No Drawing, liip'plication July 10,1951,Serial N0. 236,076

l l C laims. (Cl. 26Q92.8)

"This inventionrelates toimprovement's in'vil'lyl chloridepolymerizations. 1 y "The "polymerization of liquefiedvinyl chloride isgenerall -carried out atmildly "elevated' temperatures,aboi1t40'C."to"60 C. in 'an'aqueoi'i's '5 medium under a pressuresubstantially equal to its saturated va b pres'sure', 'i. e. about 4-'to'9 atmospheres, "in the' presence 'Of a polymerization catalyst."Pressures referred T130 Shereiii'are' absolut pressures. The.polyifieiiz'ation is generally earned to range (if .lb'o'ut "60% -17095conversion of monomer l6 3561911181. All percentages iaudpalilislliferred therinar by. light. "The polymeri zation astis Wellknown ma bean emulsion oolymeflzatien :(seeMark ,e't a1. "s. ipate'nt2,068A24, and erman Plastics "7.Ei"abti.hy De Bell, Gdggiri GIoQf,,liiib. by De Bell Richardson? Springfield, 194 p ges 157- 6)..0ragianuiarpoiymenzauen Iis'eejhightioot U.S., 1=!atent 2,51 1 ,5913 nataeimanriastics P tice," pages 66-173, and the article byRuebensaal onVinyl Resins in Chemical Engineering-for December 1950, vol. .57., pages102' 156.105); After conversion 10f the desireiiamount enamel-mopolymer, (residual unreacted Wino omefic .yinyl chloride is remoyedandthe wp dlyyzinyl chloride collected \by vvarious means} such as by mamationtortspray drying in the -casetfaquedasemu1- sionpolymeri zation;oi byLmtrauQn-in the case of -iaqueou-s v granular polymerization.iTlie. 1' sultix-ig gpolyvinyl fchlo'rideiis usually Washed with waterandi dried. M If thapolymerization {gees beyond; thje desiredconversion, ta .,pol'ymer hailing properties .:inerior. -to those[desired the i final product mayiresult particularlyrasv regards lliatand .light stability. To vla itzoidllthis, *thegbatcu :is generallycooled after the desired conversion, Uniis'ii'alfle'biesit-.iio1jymenzauori may also It placefinotl'ie row-down tankeriatue' 'stri' v ii myi hl'ofidfiiono'merfis re: e e'n -ofthe:merizatiomit'may be"necessar -waters or-1101a the-"polymer batch for o'mtime Without cooling beforepreinoving uiir acted vinyl chloride monomer;"In'this' "case the polymerization may continua during' t rage andthusigive' .a" product" mob high conversion and of resultant undesirable'pr'operti'es. also; when .unreactd wmyi tchloride "monomer removed fromthe aqueous medium, there --inay be some vinyl "chloride monomer,- a bon the "polyvinyl hloride particlesin the' aqueous "not 'r'emo edl'dryirfgof adsorbed vinyl chloon theapolyi i-nyl chlorid'ep'aii" ti'clesi -b'eforeitcanbe memovem ad- 2 versel y "affecting: the properties of"the 'finally re'coveredipolyvinyl'chloride. "It is therefore desirableto'add amaterial which "acts to terminate or shortstop the vinylchloride polymerization reaction'afterthe desired partial conversion ofpolymerizable monomer to polymer has taken place and to prevent anyfurther polymerization of the residual unreacted vinyl chloride monomer.

We have'found that a'crylonitrile and alkacrylonitriles are effectiveshortstopping agents for vinyl chloride polymerizations.

In carrying out the present invention, the conjugated nitrile is addedto the polymerization reaction after partial conversion of polymerizablemonomer to polymer (usually after about to"'% conversion) andthereaftertheunreacted-Vinyl chloride polymer is removed from theaqueous medium; and the polyvinyl chloride recoveredin the usual manner.Examples of short- -stopping agents according to the present inven-'tion are acrylonitrile,"mthacrylonitrile; and mixtures'thereof. Smallamounts of acrylonitrileor methacrylonitrile may satisfactorily be usedto shortstop the polymerization reaction, the amount effective toshortstop the polymerization generally being less than 2% based on theoriginal vinyl chloride monomer used. For practical purposes, the amountof shortstopper may be between 0.5% and 1.5% by weight of the originalvinyl chloride monomer used.

The polymerization reaction is carried out in the presence of aconventional free radical type polymerization initiator, such as aperoxygen or azo catalyst. Examples of peroxygen catalysts are inorganicperoxides, e. g. hydrogen peroxide" Tests showing -the effectiveness ofmechaniscals of the present invention-as -shortstopping agents for vinylchloride polymerizatioinwere carried out according to thefollowinjgprocedure: Intoeaich of a-n'urrib'er of crown cappedbdttles equippedwith se'lf sealing liners was placed a typical granular polymerization--re'cipe using a water-soluble ca tal yst' (1-00 parts-of liquefiedvinyl-chloride, 300' parts otwater; 0-13 part of potassium pe'rsulfate"and small amounts ofbuffering and wetting agents). Polymerizations werecarried out at 52 C. Two polymerizations served as controls to show theconversions at an intermediate polymerization (about five and one-halfhours) and at a final polymerization (about nine and one-half hours)without shortstopping agent. At the end of the intermediate and finalpolymerization times, monomeric vinyl chloride was immediately ventedand. percent conversions were obtained. In the test polymerization, 0.7part of acrylonitrile based on 100' parts of vinyl chloride monomer usedwas added to a separate polymerization bottle at the same time as theintermediate control polymeriza tion and the heating was continued tothe same overall time as the final control polymerization. Vinylchloride monomer was then vented, and

percent conversions were obtained by weighing the polymer.

The percent conversions of monomer to polymer of the control after theintermediate and final polymerization times, and the percent con-.version at the final polymerization time where the acrylonitrileshortstopper of the presentinvention was added at the intermediateconversion time, are shown in the following table:

Conversion (Percent) Shortstopper added at intermediate conversionIntermediate Final None (intermediate control) None (final control) 0.7part acrylonitrile .following table:

. .1. Conversion (Percent) shortstopper added at intermediate conversionIntermediate Final None (intermediate control) None (final control) Theabove work .shows that the acrylonitrile and methacrylonitrile of thepresent invention are efiective shortstopping agents for vinyl chloridegranular polymerizations (the experimental error in thework my be fivepercent). The chemicals of the present invention are also effective asshortstoppers for bulk or mass oil-phase vinyl chloride polymerizations,and for aqueous emulsion polymerizations which may use inorganicwater-soluble catalysts or organic monomer-soluble catalysts. In fact,granular polymerizations which use a monomer-soluble catalyst aregenerally considered to be mass polymerizations of the individual liquidmonomer globules. In aqueous emulsion and granular polymerizations, thepolymerization reaction is generally stopped at 60% to 95 conversion ofmonomer to polymer. In bulk polymerizations, the polymerization-reactionis generally stopped at lower conversions, e. g. around 40%. With theshort-stopping agents of the present invention, the -polymeriza 4 tionreaction may be stopped at any desired conversion.

In practice in emulsion polymerizations, it is a simple matter towithdraw a sample from the reaction chamber from time to time and toanalyze it for total solids in order to determine the percentconversion. On the other hand, it is almost impossible to follow theconversion in a granular polymerization by sampling, because the polymerformed separates so rapidly that a representative sample, cannot beobtained. Thus other methods of "determining the amount of conversion,and thereby the point at which the disappears (see reaction should bestopped, must be used in following polyvinyl chloride granularpolymerizations. For example, the heat evolved in the reaction mixturecan be measured and be directly correlated with the extent of conversionvia the known heat of reaction. Also experience has shown that polyvinylchloride of good physical characteristics may be obtained by stoppingthe reaction at the, pressure dropwhich is at the point Where the liquidvinylchloride monomer German Plastics Practice, pages 61 and 77). Insystemswhere the temperature in the reactor is automatically maintainedby regulation of the jacket temperature, the pressure drop willbeevidenced by a sudden pressure fall. In systems where the pressure inthe reactor is automaticallyv maintained by regulation of the jackettemperature, the pressure drop will be evidenced by a rapid rise injacket water temperature, whereupon the system is thrown out ofautomatic control and cooling water is introduced into the jacketresulting. in the usual fall of pressure in the reactor. Such methodsother than sample analyses of determining when to shortstop the reactionat the desired conversion may be used in emulsion polymerization as wellas in granular polymerization. The evolution of heat or the viscositycharacteristics may be followed in mass polymerization to determine thepoint at which the short stopping agent should be added.

The following illustrates the use of the shortstoppers of the presentinvention in batch aqueous vinyl chloride polymerizations. A typicalemulsion polymerizationreci-pe which uses a water-soluble catalyst partsofliquefied vinyl chloride, 200 parts of water, 0.2 part of potassiumpersulfate and 1.5 parts of surface-active emulsi- Tying agent), or atypical granular polymerization recipe using a water-soluble catalyst(100 parts of liquefied vinyl chloride, 300 parts of water, 0.3 part ofpotassium persulfate, and a small amount of bufiering and wettingagents), or a typical granular polymerization recip usin amonomer-soluble catalyst (100 parts of liquefied vinyl chloride, 300parts of water, 0.5'part of lauroyl per-oxide and a small amount ofsuspending agent) is agitated in aclosed jacketed reaction vessel. Thebatch is initially heated'to the desired reaction temperature between 40C. and 60 C. and maintained at the desired temperature during thepolymerization. I The pressure in the reactor at such reactiontemperatures will be irom to 9 atmospheres until the liquid vinylchloride is polymerized ajndthepressure drops. After the pressure startsto drop and before it drops 2 atmospheres, 0.5 to 1.5 part. ofacrylonitrile or methacrylonitrile per 100 parts of original vinylchloride used is added so that undesirable further polymerization isprevented} Alternatively, the sh-ortstopping agent may beadded at anydesired conversion at the discretion of the operator.zwhenwthe.desiredaconversionhasbeen reached:andtlneshortstop added, the.batchimay she transferred to the"fb.low-down or storage tank, .held:there .anydesired length :of time, :and

.then transferred to the stripper when desired .for removal of residualunreacted vinylchloride montomer. ;Finishing operations:afterresidualmono- :merremoval are .conventionalras described .in the aliteratureareierences :referred to above.

The shortstopping agents.ofzthe.presentiinventiongive a greateruniformity ;of :polymer "properties, :and

alsoaresultfinpolymersjhavinga enhance d: heat: and :light. stability.

The .shortstoppers .lOf :the present invention .;are

applicable :to .shontstopping :pf vmodified :vinyl chloride polymerswhich are madeubycopolymer- .izin g :a:major1proportion, .zgenerallyover5801% .of vinyhchloride and :up to .120 of other rmonooleate, andmixtures thereof. Such polymerizations are similar to thehomopolymerization of polyvinyl chloride but with a somewhat broaderrange of reaction temperatures from C. to 100 0., depending on theparticular vinyl chloride copolymer being made (see German PlasticsPractice, pages ,76-78). The same amount of shortstopping agent based onthe amount of vinyl chloride employed may be added after partialconversion, generally at about 60% to 95% conversion of polymerizablemonomeric material to polymeric material. 1

In view of the many changes and modifications that may be made withoutdeparting from the principles underlying the invention, reference shouldbe made to the appended claims for an understanding of the scope of theprotection afforded the invention.

Having thus described our invention, what we claim and desire to protectby Letters Patent is:

1. In the process of preparing a vinyl chloride polymer by thepolymerization of material of the group consisting of vinyl chloride andmixtures of vinyl chloride with up to 20% by weight of the vinylchloride of other mono-olefinic material which is copo'lymerizable withvinyl chloride, the step comprising adding a small amount of materialselected from the group consisting of acrylonitrile andmeth-acrylom-trile to the reaction mixture during polymerization to stopthe same after partial conversion of polymerizable monomeric material topolymeric material.

2. In the process of preparing a vinyl chloride polymer by thepolymerization of material of the group consisting of vinyl chloride andmixtures of vinyl chloride with up to 20% by weight of the vinylchloride of other monoolefinic material which is copolymerizable withvinyl chloride, the step comprising adding a small amount ofacrylonitrile to the reaction mixture during polymerization to stop thesame after partial conversion .of polymerizable monomeric material topolymeric material.

3. In the process of preparing a vinyl chloride polymer by thepolymerization of material of the group consisting of viny1 chloride andmixtures of vinyl chloride with up to 20% by weight of the vinylchloride of other monoolefinic material which is copolymerizable withvinyl chloride, the step comprising adding a small amount ofmethacrylonitrile to the reaction mixture duraeieaase ing polymerizationto stop the same after $11311 ingpolymerization to stop "the same afterabout 60% to conversionof 'vinylzchloridemonomer topolyvinyl chloride.

.5. The :method of preparing :a'vinyl chloride polymer which comprisessubjecting material of the group consisting of vinyl chlorideand-mixtures of vinyl chloride with up to 320l% by :weight of the .vinylchloride .of other monoolefinic vmaterial which is copo'lymerizable withvinyl chloride to. polymerizing conditions :inang-aqueous anedium in thepresence of a polymerization catalyst, and after about 60% to 95%conversion o'f polymerizable monomeric material topolymeric'materiaLadding to the polymerization reaction' ofito1;5%--based onthe weight of the original monomeric vinyl chloride usedof material selected from the group consisting of acrylonitrile andmethacrylonitrile to stop polymerization of unreacted polymerizablemonomeric material, and thereafter removing unreacted polymerizablemonomeric material from the aqueous medium.

6. The method of preparing a vinyl chloride polymer which comprisessubjecting material of the group consisting of vinyl chloride andmixtures of vinyl chloride with up to 20% by weight of the vinylchloride of other monoolefinic material which is copolymerizable withvinyl chloride to polymerizing conditions in an aqueous medium in thepresence of a polymerization catalyst, and after about 60% to 95%conversion of polym'erizable monomeric material to polymeric materialadding to the polymerization reaction 0.5 to 1.5% based on the weight ofthe original monomeric vinyl chloride used of acrylonitrile to stoppolymerization of unreacted polymerizable monomeric material, andthereafter removing unreacted polymerizable monomeric material from theaqueous medium.

7. The method of preparing a vinyl chloride polymer which comprisessubjecting material of the group consisting of vinyl chloride andmixtures of vinyl chloride with up to 20% by weight of the vinylchloride of other monoolefinic material which is copolymerizable withvinyl chloride to polymerizing conditions in an aqueous medium in thepresence of a polymerization catalyst, and after about 60% to 95%conversion of polymerizable monomeric material to polymeric materialadding to the polymerization reaction 0.5 to 1.5% based on the weight ofthe original monomeric vinyl chloride used of methacrylonitrile to stoppolymerization of unreacted polymerizable monomeric material, andthereafter removing unreacted polymerizable monomeric material from theaqueous medium.

8. The method of preparing polyvinyl chloride which comprises subjectingvinyl chloride to polymerizing conditions in an aqueous medium in thepresence of a peroxygen catalyst, and after partial conversion of vinylchloride monomer to polyvinyl chloride adding to the polymerizationreaction a small amount of material selected from the group consistingof acrylonitrile and methacrylonitrile to stop polymerization ofunreacted vinyl chloride monomer, and thereafter removing iinreactdvinyl chloride from'th'e aqueous me- 9. The method of preparingpolyvinyl chloride which comprises subjecting vinyl chloride to' poly-"after the pressure begins to drop and before it has dropped 2atmospheres adding to the polymerization reaction "a small amount ofmaterial selected from the group consisting of 'ac-ryloni- *trile andmethacrylonitrile to stop polymerization of unreacted vinyl chloridemonomer, and thereafter removing unreacted vinyl chloride from theaqueous medium.

.10. The method of preparing polyvinyl chloride, which comprisessubjecting vinyl chloride to polymerizing conditions in a closed vesselin the presence of a peroxygen catalyst in an aqueous medium at atemperature between 40 C. and 60 --C; under a pressure substantiallyequalto its saturated vapor pressure of about 4 to 9 atmopheres,

and after the pressure begins to drop and before it has dropped 2atmospheres adding tothe polymerization reaction a small amount ofacrylonitrile to stop polymerization of unreacted vinyl chloridemonomer, and thereafter removing unreacted vinyl chloride from theaqueousmedium. 11; The method of preparing polyvinyl chloride whichcomprises subjecting vinyl chloride to polymerizing conditionsin'aiclosed vessel in the presence of a per'oxygen catalyst in anaqueous medium at atemperatur'e between 40 C. and 60 C., under apressure substantially equal to its saturated vapor pressure of about 4to 9 atmospheres, and after the pressure begins to drop and before ithas dropped 2 atmospheres adding to the polymerization" reaction a smallamount :of methacrylonitrile' to 'stop polymerization of unreactedvinylrehloride monomer, and thereafter removing unreacted: vinylchloride from the aqueous me- :ROBERT E. COMERFORD.

" ALBERT W. 1 LEONARD F. ,MAROUS.

No references" cited.

1. IN THE PROCESS OF PREPARING A VINYL CHLORIDE POLYMER BY THEPOLYMERIZATION OF MATERIAL OF THE GROUP CONSISTING OF VINYL CHLORIDE ANDMIXTURES OF VINYL CHLORIDE WITH UP TO 20% BY WEIGHT OF THE VINYLCHLORIDE OF OTHER MONOOLEFINIC MATERIAL WHICH IS COPOLYMERIZABLE WITHVINYL CHLORIDE, THE STEP COMPRISING ADDING A SMALL AMOUNT OF MATERIALSELECTED FROM THE GROUP CONSISTING OF ACRYLONITRILE ANDMETHACRYLONITRILE TO THE REACTION MIXTURE DURING POLYMERIZATION TO STOPTHE SAME AFTER PARTIAL CONVERSION OF POLYMERIZABLE MONOMERIC MATERIAL TOPOLYMERIC MATERIAL.